In this photo released by Wildlife Conservation Society, a saiga calf runs in the Sharga Nature Reserve in Mongolia in 2006. (AP Photo/Wildlife Conservation Society, Joel Berger, HO)

(Newser)
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An already critically endangered species has been driven even further to the brink after an insane population decline compounded by the fact that scientists are at a loss to explain it. Initially, scientists weren’t too perturbed to hear some saigas—a type of antelope that inhabits Kazakhstan, Russia, and Mongolia—were dying off during their calving period in May; some 12,000 died of apparent digestive issues last year after scientists speculated that there was too much greenery, reports Live Science. But suddenly, at least 120,000 animals, or half of Kazakhstan’s population, were dead by June, including a herd of 60,000 saigas felled in four days. "I have worked in veterinary diseases all my career and I have never seen 100% mortality," an expert tells Nature. "That is extraordinary." Another adds the "extent" and "speed" of the die-off "has not been observed for any other species...It's really unheard of."

Researchers quickly moved to identify the threat, following what little clues they had: Necropsies and observations showed mothers died first, followed by their calves. But a most mysterious find came next: Scientists found toxins from the usually-harmless Pasteurella and possibly Clostridia bacteria often found in the animals’ bodies were causing extensive bleeding in their organs, per UPI. What had changed in the bacteria to make it suddenly deadly? Apparently, nothing. "There is nothing so special about it. The question is why it developed so rapidly and spread to all the animals," a researcher says. Experts are continuing to investigate but say the die-off may be another "flash crash" like the 1988 die-off of 400,000 saigas; bacteria may have spread more easily this year via standing water after a wet spring; or the Pasteurella and Clostridia bacteria may have suddenly sprung into unexpected action. (Alaska's whales aren't faring well, either.)